Automatic lead switching for ECG monitor

Abstract

A multi-lead ECG monitor which determines whether the reference electrode has been disconnected and, if so, switches to another reference electrode to continue ECG monitoring. Disconnection of the reference electrode can be determined by observing that no ECG signal is being received from any of the electrodes. When this is detected, the reference electrode is switched to another electrode which is selected in accordance with a predetermined priority scheme. After a stabilization period, the system then determines if any electrodes are still connected. If not, then, as before, it is determined that the new reference electrode is not connected and that a new reference electrode needs to be selected. The switching of the reference electrode continues in this manner until it is determined that electrodes are connected. If sufficient electrodes including the new reference electrode are still connected to the patient to permit ECG monitoring, then ECG monitoring continues and a status message is presented to the operator identifying which electrodes are disconnected. Once complete electrode connection is regained, the ECG monitor automatically switches back to the preferred settings with the desired reference electrode.

What is claimed is: 
     
       1. An electrocardiogram (ECG) monitor for detecting and displaying an ECG waveform of a patient, comprising: a plurality of electrodes including a reference electrode and at least two detecting electrodes which detect an ECG waveform of the patient;   electrode status detection means for detecting whether said detecting electrodes and reference electrode are connected to the patient and for generating electrode status signals;   reference lead switching means responsive to said electrode status signals for selecting a detecting electrode as a new reference electrode when said electrode status detection means detects that at least said reference electrode is not connected to the patient and for selecting electrodes of said plurality of electrodes to be used to generate a common mode drive signal for application to said new reference electrode; and   means for processing ECG waveforms acquired from said detecting electrodes in response to application of a common mode drive signal to said new reference electrode and for displaying said ECG waveforms to an operator.   
     
     
       2. A monitor as in claim 1, further comprising a common mode signal generating circuit including means for generating sum signals from combinations of signals output by detecting electrodes and means responsive to said reference lead switching means for selecting a sum signal corresponding to the currently available detecting electrodes and for generating common mode drive signals for driving either said reference electrode or said new reference electrode. 
     
     
       3. A monitor as in claim 2, further comprising a common mode drive select circuit for applying a common mode drive signal from said common mode signal generating circuit to the electrode selected by said reference lead switching means as the new reference electrode. 
     
     
       4. A monitor as in claim 3, wherein said reference lead switching means comprises a microprocessor responsive to said electrode status signals to determine whether the reference electrode is connected to the patient and to select one of the detecting electrodes as the new reference electrode when it is determined that the reference electrode is not connected to the patient. 
     
     
       5. A monitor as in claim 4, wherein said microprocessor removes the reference electrode from the electrode status signals when the new reference electrode is selected. 
     
     
       6. A monitor as in claim 4, wherein said microprocessor sends a common mode drive select signal to said common mode drive signal generating circuit in accordance with the electrodes said microprocessor determines to be connected to the patient. 
     
     
       7. A monitor as in claim 4, wherein said microprocessor sends a reference electrode select signal to said common mode drive select circuit to instruct said common mode drive select circuit to apply said common mode drive signal to the new reference electrode. 
     
     
       8. A monitor as in claim 4, wherein said processing means comprises instrumentation amplifiers for amplifying ECG waveforms received from said detecting electrodes, and said microprocessor sends an ECG waveform select signal to said instrumentation amplifiers to select the ECG waveforms for display. 
     
     
       9. A modular patient monitor for monitoring selected vital signs of a patient, said patient monitor comprising at least one removable electronic module for processing vital signs data from said patient and a display for displaying the processed vital signs data, wherein said at least one removable electronic module comprises an electrocardiogram (ECG) module which detects and processes ECG waveforms received from a plurality of electrodes including a reference electrode and at least two detecting electrodes which detect an ECG waveform of the patient, said ECG module comprising: electrode status detection means for detecting whether said detecting electrodes and reference electrode are connected to the patient and for generating electrode status signals;   reference lead switching means responsive to said electrode status signals for selecting a detecting electrode as a new reference electrode when said electrode status detection means detects that at least said reference electrode is not connected to the patient and for selecting electrodes of said plurality of electrodes to be used to generate a common mode drive signal for application to said new reference electrode; and   means for processing ECG waveforms acquired from said detecting electrodes in response to application of a common mode drive signal to said new reference electrode and for displaying said ECG waveforms to an operator.   
     
     
       10. A monitor as in claim 9, said ECG module further comprising a common mode signal generating circuit including means for generating sum signals from combinations of signals output by detecting electrodes and means responsive to said reference lead switching means for selecting a sum signal corresponding to the currently available detecting electrodes and for generating common mode drive signals for driving either said reference electrode or said new reference electrode. 
     
     
       11. A monitor as in claim 10, said ECG module further comprising a common mode drive select circuit for applying a common mode drive signal from said common mode signal generating circuit to the electrode selected by said reference lead switching means as the new reference electrode. 
     
     
       12. A monitor as in claim 11, wherein said reference lead switching means comprises a microprocessor responsive to said electrode status signals to determine whether the reference electrode is connected to the patient and to select one of the detecting electrodes as the new reference electrode when it is determined that the reference electrode is not connected to the patient. 
     
     
       13. A monitor as in claim 12, wherein said microprocessor removes the reference electrode from the electrode status signals when the new reference electrode is selected. 
     
     
       14. A monitor as in claim 12, wherein said microprocessor sends a common mode drive select signal to said common mode drive signal generating circuit in accordance with the electrodes said microprocessor determines to be connected to the patient. 
     
     
       15. A monitor as in claim 12, wherein said microprocessor sends a reference electrode select signal to said common mode drive select circuit to instruct said common mode drive select circuit to apply said common mode drive signal to the new reference electrode. 
     
     
       16. A monitor as in claim 12, wherein said processing means comprises instrumentation amplifiers for amplifying ECG waveforms received from said detecting electrodes, and said microprocessor sends an ECG waveform select signal to said instrumentation amplifiers to select the ECG waveforms for display to the operator on said display. 
     
     
       17. A method of detecting an ECG waveform of a patient, comprising the steps of: applying a plurality of electrodes to the patient, the electrodes including a reference electrode and at least two detecting electrodes which detect an ECG waveform of the patient;   applying a drive signal to the reference electrode;   detecting whether said detecting electrodes and reference electrode are connected to the patient;   selecting a detecting electrode as a new reference electrode when it is determined in said detecting step that at least said reference electrode is not connected to the patient; and   applying a new drive signal to the new reference electrode.   
     
     
       18. A method as in claim 17, comprising the further steps of generating sum signals of the ECG waveforms received from combinations of detecting electrodes available after said selecting step, selecting a sum signal corresponding to the ECG waveforms from the detecting electrodes available after said selecting step, and generating common mode drive signals for driving said new reference electrode in said new drive signal applying step. 
     
     
       19. A method as in claim 17, wherein said detecting step comprises the step of determining which detecting electrodes are outputting ECG waveforms and said selecting step comprises the steps of determining whether the reference electrode is connected to the patient and selecting one of the detecting electrodes as the new reference electrode when it is determined that the reference electrode is not connected to the patient. 
     
     
       20. A method as in claim 17, comprising the further steps of indicating to an operator which electrodes are connected to the patient and displaying the ECG waveforms desired by the operator, if such waveforms are available.